A vehicle body structure of this type is disclosed in Japanese Patent Laid-Open Publication No. 2000-108949, for example. This vehicle body structure will be described with reference to FIG. 19 hereof.
A vehicle body 200 shown in FIG. 19 includes a floor tunnel 201 extending longitudinally in the center of the vehicle width, right and left side sills 202 (only one is shown.) provided on the opposite sides of the vehicle body and extending longitudinally, and right and left floor panel portions 203, 203 interposed between the floor tunnel 201 and the side sills 202.
A propeller shaft 211 is extended through the inside of the floor tunnel 201. The propeller shaft 211 is mounted to the inside of the floor tunnel 201 with reinforcing members 212, 212 and a bracket 213.
A crossmember 214 is extended across the floor tunnel 201 between the right and left side sills 202. Right and left brackets 215, 215 for mounting a sheet (not shown) are provided on the right and left floor panel portions 203, 203, respectively. Reference numeral 216 denotes a handbrake device.
In some types of vehicles, an engine is mounted to the front of a vehicle body via a subframe, and a propeller shaft is not extended through a floor tunnel. In such types of vehicles, however, various types of equipment such as a muffler is sometimes disposed below a front half portion of a floor tunnel. Therefore, a floor tunnel protruding upward for various types of equipment cannot be completely eliminated. It is, however, possible to reduce the height of a rear half portion of the floor tunnel. The reduced height of the rear half portion of the floor tunnel results in a larger passenger compartment and improved comfort. It is especially effective for low-floor type vehicles, for which it is desired to reduce the height of a rear half portion of a floor tunnel to make a passenger compartment larger.
When collision energy acts on the front of a vehicle body, plastically deforming the vehicle front, a subframe mounted to the vehicle front and an engine mounted on the subframe are moved rearward. The engine located in a higher level than the subframe strikes a front upper edge of a floor tunnel, producing collision energy acting on the front upper edge. Also, collision energy acts from the retreated low-level subframe on a front lower edge of the floor tunnel. In this manner, collision energy is transmitted from both the retreated high-level engine and low-level subframe to the floor tunnel. It is required to efficiently transmit the collision energy to the front of the vehicle body.
Now, a conventional vehicle body structure in which floor frame members are provided to increase the rigidity of a floor panel and to increase the rigidity of an entire vehicle body will be described with reference to FIGS. 20 and 21.
A vehicle body 300 shown in FIG. 20 includes a floor tunnel 301 provided in the center of the vehicle width and extending longitudinally, right and left floor frame members 302, 302 disposed on the right and left of the floor tunnel 301 and extending longitudinally, and right and left side sills 303, 303 provided outside of the right and left floor frame members 302, 302 and extending longitudinally.
Right and left front side members 304, 304 extend forward from the front ends of the right and left floor frame members 302, 302. A floor panel 305 (see FIG. 21) integrally continuous with the floor tunnel 301 is placed on and joined to the right and left floor frame members 302, 302. Reference numerals 306, 306 denote outriggers.
Collision energy acting on the front of the vehicle body 300 is transmitted and dispersed from the front side members 304, 304 through the floor frame members 302, 302 to the floor panel 305 (see FIG. 21), and is further transmitted from the floor panel 305 to the floor tunnel 301. The floor frame members 302, 302 are retreated by the collision energy, causing a force for deforming the floor panel 305 rearward from the floor tunnel 301 of relatively high rigidity.
When the vehicle front is plastically deformed by collision energy acting on the front of the vehicle body 300, a subframe 308 mounted to the front of the vehicle body 300 and an engine 307 mounted on the subframe 308 are moved rearward. As a result, the subframe 308 and the engine 307 strike the front end of the floor tunnel 301, applying the collision energy to the front end of the floor tunnel 301. The collision energy is transmitted and dispersed from the floor tunnel 301 to the floor panel 305, and is further transmitted from the floor panel 305 to the floor frame members 302, 302.
It is difficult to configure the floor tunnel 301 and the floor frame members 302, 302 so that the amount of plastic deformation of the floor tunnel 301 is equal to the amount of retreat and the amount of plastic deformation of the floor frame members 302, 302 when collision energy acts on the floor tunnel 301 as described above. Therefore, the floor panel 305 can deform between the floor tunnel 301 and the floor frame members 302, 302. Large deformation of the floor panel 305 (e.g., development of large creases) affects the joined state of the floor panel 305 to the floor tunnel 301 and the floor frame members 302, 302.
In order to avoid such influence, it may be conceived to reinforce low-rigidity portions with reinforcing members. However, it unfavorably complicates the configuration of the vehicle body 300 and also increases the vehicle weight.
In this context, it is desired to prevent difference in displacement between a floor tunnel and floor frame members even when the front of a vehicle body receives collision energy, avoiding increase in the weight of the vehicle body with a simple configuration.